1. Field of the Invention
The present invention relates to an improved shunt having a measuring circuit optimized to compensate for errors caused by skin effect and proximity effect of the shunt, and particularly to a rectangular shaped shunt element.
2. Description of Prior Art
A shunt functions on the principle that the passage of current therethrough produces a potential drop across the shunt and that this drop or difference in potential permits, by Ohm's law, to calculate the intensity of the current flowing therethrough. The measuring circuit to collect this potential drop measurement is constituted by a wire which is isolated within the shunt and inserted within a groove provided with the resistive material, thus constituting a monolithic shunt with a wire embedded therein.
There are two factors that can limit the utilization of a shunt:
(1) the error caused by the variation of the temperature of the resistive material; and
(2) the error caused in the response of a shunt to the step current and which is caused by skin, or proximity effects.
A variation in the temperature of the resistive material of the shunt also gives rise to a variation of the nominal value of the shunt because the thermal coefficient of the resistivity is not nil. The adiabatic heating of the shunt in a short circuit mode determines the quantity of resistive material required, whilst heating of the shunt in its continuous operation determines the geometry thereof. The shunt of the present invention has a rectangular geometry which offers an efficient heat dissipation and permits the passage of a permanent high current therethrough.
The response obtained at the output of the shunt should ideally be a replica of the variable current applied at its input. The response of a standard shunt always differs from the measured current due to skin effect in the resistive material, and also due to the proximity of the shunt to the heavy current circuits.